A desire of a cellular telephone user is to have a single cellular telephone that can operate anywhere in the world: a “world” phone. Unfortunately, in order to operate at different locations throughout the world, the world phone needs to be able to communicate with different cellular communications networks, each using a potentially different communications mechanism, as well as being able to tune its oscillator to different frequency ranges. This is due to the wide variety of communications standards and frequency bands being used in different areas of the world. For example, in the United States, it is common to encounter GSM (Global System for Mobile Communications), CDMA (Code Division Multiple Access), TDMA (Time-Division Multiple Access), digital cellular system (DCS), and personal communications service (PCS) cellular telephone networks. These multiple types of cellular telephone networks may use multiple frequency ranges, such as the 850 and 900 MHz frequency ranges as well as the 1.8 and 1.9 GHz frequency ranges on up to over 2.7 GHz. In other areas of the world, other types of cellular telephone networks and frequency ranges may be in use.
One solution to the problem of tuning an oscillator to such a wide variety of frequency ranges is to use multiple oscillators, with one oscillator for each frequency range of interest. With multiple oscillators, each oscillator may be optimized for each frequency range, potentially maximizing tuning accuracy.
Another solution to the problem is to use a single oscillator but with multiple oscillator cores or LC tanks. The multiple oscillator cores or LC tanks may be used to extend the tuning range of the single oscillator without needing multiple oscillators. Each of the multiple oscillator cores or LC tanks may be switched into use when needed. Again, the use of multiple oscillator cores or LC tanks may allow for the optimization of oscillator performance for the different frequency ranges in use.
Yet another solution to the problem is to use a switch (or switches), such as a CMOS switch, to short circuit a portion of an inductor to increase the tuning range of the local oscillator. The short circuiting of a portion of an inductor may alter the inductance of the inductor, thereby changing the tuning range of the oscillator. The use of the switch may permit the use of a single local oscillator.